1 April 2017

There is a wide-held belief that people who consume too much added refined sugar will develop diabetes. Similarly, there is a common belief that people with diabetes need to limit or avoid added sugar to manage their condition. To help address these common diabetes myths, two globally recognised experts on sugars (Dr Mike Lean and Dr Lisa Te Morenga) recently reviewed the evidence for the British Medical Bulletin. They analysed the evidence using four theoretical rationales for why, in principle, added sugars might be of concern with respect to (type 2) diabetes.

1. Sugar causes, or contributes to causing, diabetes.

There is a lack of experimental evidence from randomised controlled trials in humans for a causal role for added sugars in the development of type 2 diabetes (T2DM). There is an association between consuming 1–2, 355 mL regular (i.e., 10% added sugars) sugar-sweetened beverages (SSBs) a day and the risk of developing type 2 diabetes in observational studies, but it is “...small and substantially reduced when data are adjusted for BMI [Body Mass Index].” There are also associations between consuming intensely (“artificial”) sweetened beverages and risk of type 2 diabetes, but there isn’t an association between fruit juices (which contain around 10% sugars) and risk of diabetes. “These studies provide strong evidence that the association between SSBs and T2DM relies on associated lifestyles and patterns of food and drink consumption, rather than on the sugar itself.”

They conclude that: “given the multifactorial causes of weight gain, sugar reduction as a stand-alone action is unlikely to impact strongly on diabetes incidence.”

2. Sugar consumption aggravates glycemia with diabetes.

Randomised controlled trials do not provide any evidence that consumption of added sugars has any detrimental impact on blood glucose management in people with type 1 or type 2 diabetes, and there is in fact some evidence that moderate consumption (less than 60g per day, or around 10% of energy) may improve glycemic control.

They conclude that: “despite a common assumption that sugar must be hazardous for people with T2DM, the evidence says otherwise.”

Randomised controlled trials provide evidence that when people with and without diabetes are given large amounts (average of 124 grams per day, or around 24% of energy) of free sugars their total, LDL and HDL cholesterol, and triglycerides, increase slightly (0.02–0.16 mmol/L), and their diastolic blood pressure increases (1.4 mm Hg). However, despite these small but statistically significant effects on cardiovascular disease risk factors “Studies among people with diabetes found no effect of SSBs on heart disease.”

They conclude that: “the evidence supports limitation of free sugar to 10% EI [energy intake] to reduce macrovascular complications for people with T2DM.”

High blood glucose increases the risk of microvascular complications of diabetes like retinopathy, neuropathy and nephropathy. However, there is no evidence from randomised controlled trials that sugars increase the risk of microvascular complications of diabetes.

They conclude that: “Reducing glycaemia does reduce the progression of microvascular complications of T2DM, but the relatively low glycaemic index of sucrose would not suggest any special role.”

Lean and Te Morenga’s overall conclusion

“The media noise generated by belief-based claims that sugar is as toxic and addictive as tobacco or heroin arises from a poor grasp of scientific methods and evidence. The media debate has also undermined consumer understanding of healthy nutrition. There is now a widespread belief that sugar is the sole cause of rising rates of obesity and diabetes. This, unfortunately, plays directly into the hands of the food industry, by providing new opportunities for it to peddle highly processed nutrient-poor foods to confused and concerned consumers.”

Sugar does not cause diabetes and people with diabetes do not need to avoid it completely. However, it’s prudent to consume less than 10% of energy from added/free sugars to limit unwanted calories and reduce the risk of tooth decay whether or not you have diabetes.

Alan Barclay, PhD is a consultant dietitian. He worked for Diabetes Australia (NSW) from 1998–2014 and is a member of the editorial board of Diabetes Management Journal (Diabetes Australia). He is author/co-author of more than 30 scientific publications, and co-author of The Low GI Diet: Managing Type 2 Diabetes (Hachette Australia) and The Ultimate Guide to Sugars and Sweeteners (The Experiment, New York). You can read a review of his latest book, Reversing Diabetes (Murdoch Books), in Glycosmedia Diabetes News.